Re: [Harp-L] Reed Slot Tolerance



Yes, the normal clearance is about .001"

What tools do you have in mind when you say "hobbyist-level tools"?  

If a tool has an accuracy specification or tolerance of .001", that means that the cut on the workpiece can be as much as .001" from the dimension on the drawing.  Few machine tools...even professional ones... are that accurate.  That means that the clearance could be anywhere from zero to twice the desired .001". 

You might achieve the necessary accuracy using a wire EDM machine on a stainless steel reedplate.  I don't know of any milling machine that could be that accurate.  Obviously an EDM machine is very expensive and requires expert operation.  It could hardly be classified as "hobbyist level." 

It is conceivable that you could use a machine tool to rough cut an undersized slot with round corners and hand-file it to its final dimensions.  Then you need to be able to very accurately measure slot width and length.  A hand caliper isn't adequate.  I would make a set of taper gauges and calibrate them with a micrometer that can be read to .0001" You would need a separate taper gauge for each length and each width of the slots. 

Assuming that you have created an acceptable slot, you still need to drill a rivet/screw hole on the slot centerline and the proper  distance from the end of the slot.  Position errors must be much less than .001" or the reed won't align with the slot. Accurately locating the rivet hole is not a trivial problem.

 Although this is possible, it is ticklish and time consuming work even for an experienced machinist.   Making a dozen such slots in a reedplate, even if possible, would be a daunting task. 

In an industrial setting, all of this time and trouble can be lavished on a punch and die.  Then the slots can be accurately punched in the plates in one whack of the press.

You can actually use a blade as thick as .002" in the slot without damaging the reed.  This is because the reed is flexible and deflects out of the way of the blade. When using a .002" blade, I don't push it too near the rivet end where the reed is much less flexible.  With a .001" blade, there is absolutely no worry.

Vern

On Dec 3, 2009, at 9:50 AM, Robert Coble wrote:

> 
> I know I have seen several references to using a 0.001" shim to run down the sides of a reed to make sure there are no burrs on the edge and also that the reed is seated in the middle of the slot.
> 
> Would this not imply that the normal clearance/tolerance between reed edge and reedplate edge is 0.001"? If so, then the manufacturing tolerance obviously is not impossible to obtain with hobbyist-level tools, which have at least that capability (on paper, if not in fact). If the tolerance is smaller, then wouldn't using a 0.001" shim cause some sort of misalignment or deformation?
> 
> 
> Help, please,
> Crazy Bob 		 	   		  






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